The process and apparatus of the invention relate to processing waste water from nuclear power reactors and other sources of water contaminated with radionuclides and other interfering materials and/or contaminates. In particular, the present process and apparatus are related to processing waste waters contaminated with colloidal, suspended and dissolved radionuclides and other contaminates.
In the commercial nuclear power industry, there are primarily two types of reactor systems used in Nuclear Power Plants (NPP's), namely boiling water reactors (BWR's) and pressurized water reactors (PWR's). Both use water to moderate the speed of neutrons released by the fissioning of fissionable nuclei, and to carry away heat generated by the fissioning process. Both also use water to generate steam for rotating the blades of a turbine generator. Water flows through the reactor core, is recycled, and inevitably becomes contaminated with iron (Fe-55), nickel (Ni-63), colloidal and soluble cobalt (Co-58, and Co-60), cesium (Cs-137), and other radionuclides. The water further becomes contaminated with non-radioactive organics, e.g., oils, greases and total organic carbon (TOC), biologicals, and colloids (e.g., iron rust).
In a boiling water reactor (BWR), the water passing through the core will be used directly as steam in driving turbine-generators for the production of electricity. In a pressurized water reactor (PWR), the primary water that flows through the reactor is isolated by steam generators from the secondary water that flows through the turbine generators. In both cases, while the chemical constituents of the waste water will be different, these reactor systems will produce radionuclides and colloidal, suspended and dissolved solids that must be removed before the waste water may be reused or released to the environment.
The presence of iron (as iron oxide from carbon steel piping) in Boiling Water Reactor (BWR) circuits and waste waters is a decades old problem. The presence and buildup of this iron in condensate phase separators (CPS) further confounds the problem when the CPS tank is decanted back to the plant. Iron carryover here is unavoidable without further treatment steps. The form of iron in these tanks, which partially settles and may be pumped to a de-waterable high integrity container (HIC), is particularly difficult and time-consuming to dewater. Adding chemicals upstream from the CPS, such as flocculation polymers, to precipitate out the iron only produces an iron form even more difficult to filter and dewater. For example, such chemically pretreated material contains both floc particles of sizes up to 100 microns and also submicron particles. It is believed that the sub-micron particles penetrate into filter media, thus plugging the pores and preventing successful filtration of the larger micron particles.
Like BWR iron-containing waste waters, fuel pools, or “basins,” (especially during the decontamination phase) often contain colloids which make clarity and good visibility nearly impossible. Likewise, miscellaneous, often high-conductivity, waste steams at various plants contain such colloids as iron, salts (sometimes via seawater intrusion), dirt/clay, surfactants, waxes, chelants, biologicals, oils and the like. Such waste streams are not ideally suited for standard dead-end cartridge filtration or cross-flow filtration via ultrafiltration media (UF) and/or reverse osmosis (RO), even if followed by demineralizers. Filter and bed-plugging by these various compounds are almost assured.
According to the Nuclear Energy Institute1, America's nuclear power plants (NPPs) generate more than half the volume of the nation's low-level radioactive waste (LLRW). The LLRW from the NPPs typically includes water purification filters and resins, tools, protective clothing, plant hardware, and wastes from reactor cooling water cleanup systems. Depending on the class of the LLRW (designated as classes A, B, and C by the Nuclear Regulatory Commission), the LLRW may be sent for disposal either to the Barnwell site in South Carolina or to the Clive, Utah, site of Energy Solutions (ES), formerly the Environcare Utah site. Barnwell accepts all classes of LLRW, whereas ES currently is approved only for Class A waste, which has the lowest activity limits of the three classes.
The Barnwell site is scheduled for closure in 2008. Consequently, if ES has not received approval for disposal of Class B and C wastes by that time, it is imperative that LLRW generators minimize or eliminate the production of these waste classes and produce only Class A wastes or face indefinite on-site storage of wastes exceeding Class A limits. Should ES eventually be approved for disposal of the higher activity wastes, production of Class A wastes will still be advantageous to LLRW waste generators because of the lower cost of disposal of this less hazardous class of wastes.
Class A waste, depending on the constituents and activity, can be disposed of in either bulk trench or containerized trench and makes up nearly 80% of the market. As pointed out previously, Energy Solutions of Utah can currently take only Class A waste. Furthermore, even though Barnwell can take Class A, B, and C wastes at the present time, this site is scheduled to close in 2008. In reality, the disposal classification at ES, and nationwide, is more complicated than this simplified picture. There are actually four (4) classifications of radioactive wastes as defined by 10 CFR 61.55. Determination of a waste's classification is based on the concentrations of specific long-lived radioisotopes listed in Table 1 of 10 CFR 61.55 and of specific short-lived isotopes listed in Table 2 of 10 CFR 61.55.
Utilizing Tables 1 and 2 in the Utah Waste Classification System from the Utah Administrative Code (UAC) R313-15-1008, along with the stipulations outlined in 10 CFR 61.55, wastes are determined to be Class A, Class B, Class C, or Greater Than Class C (GTCC). The Utah Waste Classification System is similar to the NRC Waste Classification System in 10 CFR 61.55, except that it includes Radium-226 as a Table 1 radionuclide. Class A is the least hazardous waste class and GTCC is the most hazardous. The waste is Class A if it does not contain more than the indicated amounts of the isotopes listed in Tables 1 and 2. A compilation of Tables 1 and 2 as shown in Table I below entitled Classification of Low-Level Radioactive Waste. Table I illustrates the concentration limits for low-level radioactive waste.
TABLE IClassification of Low-Level Radioactive WasteConcentration LimitRadionuclideClass AClass BClass CTotal of t½ >5 yrs. (Ci/m3)700Nonenone3H (Ci/m3)40Nonenone14C (Ci/m3)0.8814C in activated metal (Ci/m3)88059Ni in activated metal22220(Ci/m3)60Co (Ci/m3)700Nonenone63Ni (Ci/m3)3.57070063Ni in activated metal357007000(Ci/m3)90Sr (Ci/m3)0.04150700094Nb in activated metal0.020.2(Ci/m3)99Tc (Ci/m3)0.33129I (Ci/m3)0.0080.08137Cs (Ci/m3)1444600TRU with t½ >5 yrs.10100(nCi/g)241Pu (nCi/g)3503,500242Cm (nCi/g)2,00020,000226Ra (Ci/m3)10100
There are a number of prior art techniques used for removal of radionuclides and colloidal, suspended and dissolved solids, and the requirement to remove such materials from waste waters is not unique to nuclear reactors. However, the nature of nuclear reactors raises special concerns about the use of additives for chemical treatments because of the desire to avoid adding any chemical compounds that might make the radioactive wastes also hazardous chemical wastes. Waste that is both radioactive and chemically hazardous is referred to as mixed waste.
There are other concerns as well. The processed waste water must be quite free of radioactive contaminants if it is to be released to the environment. The radioactive material extracted from the waste water during processing must be stable or in a form that can be stabilized for disposal in a way that meets disposal site requirements, particularly with respect to preventing the leaching out of radioactive contaminates by liquid water. In addition, the final cleanup of the waste water often employs demineralizers containing ion exchange resins and other ion removal media and, as explained further below, it is highly desirable that the buildup of radionuclides on these media be restricted to radioactivity levels (measured in Curies) that do not exceed the limits established for Class A waste in order to permit disposal of depleted resins at repositories licensed to receive such wastes. Finally, the volume of radioactive wastes of all classifications must be minimized because of both the limited space available for disposal of these wastes and the high cost of their disposal.
Water processing media (ion exchange resins, adsorbents, activated carbon, zeolites, etc.) are an important part of systems that remove radionuclides and other contaminants from waste water. Replacement of these media is needed when they become saturated with contaminants to the extent that their usefulness is significantly impaired, i.e., they must go out of service on either capacity, radiation dose or differential pressure.
Spent ion exchange (IX) resins and other media from demineralizers therefore represent a significant portion of the LLRW produced by NPPs. When treating plant waste waters, these media often are depleted by the non-radioactive ionic species, which may be at higher concentrations than the radioactive species by numerous orders of magnitude. After media dewatering, samples of the spent media bed are taken and analyzed to determine the class for disposal. Obviously, the lower the concentration of non-radioactive ionic species, the higher is the chance that the media bed will be greater than Class A.
Past practice to minimize costs has been to load demineralizer media with contaminants to the maximum extent feasible before removal. However, recent increases in disposal site fees and future site closures for Class B and C wastes have effectively nullified this strategy. Disposal fees for Class B and C wastes are now sufficiently higher than for Class A waste that it is most cost-effective to remove demineralizer media before they exceed the Class A limit. Further, the main site for disposal of Class B and C wastes in Barnwell, S.C., is being completely phased out from taking waste from most states by Jun. 30, 2008. These two factors drive a need for more effective strategies for managing radioactive wastes and, in particular, reducing the amount of Class B and Class C wastes.
Accordingly there is a need for better ways of processing radioactive waste water containing contaminants in the form of dissolved ions and/or suspended solids, both radioactive and non-radioactive, from nuclear power reactors and other sources.